UNITED NATIONS (AP) ' International envoy Kofi Annan told the U.N. Security Council Thursday that despite the fragile cease-fire in Syria, the government has failed to implement the council demand that it withdraw troops and heavy weapons from cities and towns, U.N. diplomats said.

The diplomats, speaking on condition of anonymity because Annan's briefing was behind closed doors, said the joint U.N.-Arab League envoy urged the Security Council to demand that Syrian President Bashar Assad order his troops back to barracks.

In a statement issued before the briefing, Annan said he was "encouraged" that a cease-fire appeared to be holding and asked for speedy deployment of an observer mission to help keep the peace.

The diplomats said the council was discussing a resolution on deployment of an observer mission which could be adopted as early as Friday. South Africa's U.N. Ambassador Baso Sangqu said discussions on the text would begin Thursday afternoon.

Annan and U.N. Secretary-General Ban Ki-moon urged the Syrian government to keep its promises to implement the envoy's six-point peace plan.

Ban told a news conference in Geneva that a single gunshot could derail the fragile peace and that it was up to Syria to maintain the cease-fire.

"As of this moment the situation looks calmer. We are following it very closely," Ban said.

"The world is watching, however, with skeptical eyes, since many promises previously made by the government of Syria had not been kept. The onus is on the government of Syria to prove that their words will be matched by their deeds at this time," he said.

Shortly after the 6 a.m. deadline passed Thursday, there was no sign of heavy shelling or rocket attacks in Syria. But a civilian was reported killed and Syria's state-run news agency said "terrorist groups" detonated a roadside bomb that killed a soldier.

The Assad regime's crackdown on mass protests began more than a year ago.

Annan, also in Geneva, said in a statement that he also was encouraged that the cease-fire in Syria appeared to be holding and urged the government and rebels to fully implement his 6-point peace plan.

Annan stressed just before his videoconference with the U.N. Security Council that the plan includes military provisions requiring the withdrawal of troops and heavy military equipment from towns and cities and a commitment to move to a political process.

The council was being asked to approve the deployment of a U.N. observer mission as soon as possible to allow for "a serious political dialogue" to be launched quickly.

"It is difficult to fully assess the situation on the ground, in the absence of U.N. observers. And therefore we are working with the Security Council to send an observer team as promptly as possible," Ban told reporters.

The council's major powers ' the U.S., China, Russia, Britain and France ' all hold veto power on the 15-nation council, where Russia has served as Syria's key ally.

"If we are to stop Syria's descent into chaos, the international community must speak and act as one," Ban said.

Annan's spokesman, Ahmad Fawzi, has told reporters that the U.N.-backed mission would have about 200 to 250 observers and that nations were being asked to contribute soldiers.

Ban said the observer mission could get going almost as soon as it gains authorization and that he expects Russia to support it, based on talks with Foreign Minister Sergey Lavrov on Wednesday.